Brachytherapy is a form of internal radiation treatment where radioactive sources are placed on or within cancerous tumors. There are two major forms of brachytherapy: permanent seed implantation, wherein radioactive seeds are permanently placed within a cancerous gland or tissue mass, and high dose rate (HDR) temporary brachytherapy, which involves the temporary placement of a high intensity radiation source within or in close proximity to the cancerous tumor.
HDR temporary brachytherapy is particularly suited for treatment of prostate, gynecologic, breast, head and neck, lung, esophageal, bile duct, anorectal and sarcoma cancers. Tiny plastic catheters are placed in the subject tissue mass for administration of a series of radiation treatments. A computer-controlled machine, often referred to as an “afterloader,” loads a highly radioactive seed, typically made of iridium, into each of the catheters in a serial fashion. The radiation dose delivered to a particular zone of the affected tissue mass may be tailored by altering the time the seed is allowed to dwell in a particular catheter—a significant advantage of HDR temporary brachytherapy over permanent seed implantation. The catheters are removed upon completion of the treatment series.
Minimization of exposure of certain regions of an affected tissue mass, as well as non-cancerous neighboring tissue, is typically desired during the HDR temporary brachytherapy. For example, in the treatment of prostate cancer, it is advantageous to minimize the exposure of the urethra and rectum during HDR treatment. Generally, directing the intensity of the radiation dose toward the cancerous tumor while reducing the intensity directed away from the tumor is desired.